Let the unknown side be x.
Perimeter of the triangle = sum of its three sides
⟹8m2−9m+4 = (3m2−5m) + (4m2+12) +x
⟹x = (8m2−9m+4)−(3m2−5m)−(4m2+12)
⟹x = 8m2−9m+4−3m2+5m−4m2−12
⟹x = 8m2−4m2−3m2−9m+5m+4−12
⟹ x = m2−4m−8
Find the third side of a triangle whose perimeter is 8m2−9m+4 and two of its sides are 3m2−5m and 4m2+12.
Find the third side of a triangle whose two sides are (3m2−5m) and (4m2+12) and perimeter is (8m2−9m+4).